import torch
import torch.nn as nn
import torch.nn.functional as F

import math

class PositionalEncoding(nn.Module):

    def __init__(self, d_model, dropout, max_len=5000):
        super(PositionalEncoding, self).__init__()
        self.dropout = nn.Dropout(p=dropout)


        pe = torch.zeros(max_len, d_model)
        position = torch.arange(0., max_len).unsqueeze(1)
        div_term = torch.exp(torch.arange(0., d_model, 2) * -1 * (math.log(10000.0) / d_model))
        pe[:, 0::2] = torch.sin(position * div_term)
        pe[:, 1::2] = torch.cos(position * div_term)

        pe = pe.unsqueeze(0)
        self.register_buffer('pe', pe)
    
    def forward(self, x):
        
        x = x + self.pe[:, : x.size(1)].clone().detach().requires_grad_(False)

        return self.dropout(x)


